Hypersensitivity Pneumonitis (HP), or extrinsic allergic alveolitis, is an interstitial lung disease that develops following repeated exposure to inhaled environmental antigens. The disease is characterized by alveolitis and granuloma formation that in some patients progresses to fibrosis. The development of fibrosis in HP is associated with high morbidity rates;unfortunately the lack of information on disease pathogenesis has limited the development of therapies to treat the disease. Additionally, the disease is frequently misdiagnosed due to the variability of disease symptoms, differing diagnostic criteria, and a lack of understanding of the environmental antigens and host/genetic risk factors that lead to disease. Our laboratory has been studying the role of IFN( in the development of HP using the Saccharopolyspora rectivirgula (SR) animal model. IFN( is a Th1 cytokine that is required for the development of granulomas in the lungs of mice following repeated exposure to SR. The production of IFN( is important for the expression of T cell chemokines that recruit T cells into the lung following SR exposure;in the absence of IFN(, T cell recruitment and subsequently granuloma formation are reduced. Therefore the cells that produce or regulate IFN( production following SR exposure play a pivotal role in disease pathogenesis. Our studies have revealed that neutrophils are a source of IFN( during the early stages of HP and depletion of neutrophils prior to SR exposure results in decreased IFN( expression. These results suggest that neutrophils play a critical role in the development of HP and understanding the mechanisms that regulate neutrophil recruitment and production of IFN( may provide important new insights into disease pathogenesis. The goals of the proposed study are: Specific Aim1 - to understand the role of neutrophils in driving IFN( production in the lung following SR exposure. Specific Aim 2 - to determine the role of pattern recognition receptors in neutrophil recruitment into the lung.